Need some help

[Dadinos]

I use this repository to verifiy incomming and outgoing json requests and responses.
I want to rework the error output to another json format.

Currently it is, as example:

Error 400: 
{
    "message": "Request validation failed",
    "errors": [
        {
            "name": "catalogus",
            "code": "error_format",
            "value": "",
            "in": "query",
            "type": "string",
            "format": "uri"
        }
    ]
}

I tried to catch this error so i can modify the repsonse like this:

$mw = new HKarlstrom\Middleware\OpenApiValidation(__DIR__.'/catalog_openapi.json');
$mw->addFormat('string','duration',new myDurationFormat());

$options = [
		'validateRequest'=> false,
		'exampleResponse' => true,
		 'beforeHandler' => function (\Psr\Http\Message\ServerRequestInterface $request, array $errors) : \Psr\Http\Message\ServerRequestInterface {
			// Alter request modifiy the json reponse here !!!
			echo "tadaaaa"; <- never outputted
			return $request;
		}
	];

And finally in my route:

$app->get('/v1/zaaktypen[/{params:.*}]',\App\Action\ZTCZaaktypenAction::class)->add($mw,$options);

But it never touches the before- or errorHandler.

Any ideas how to get this working?